Place white chocolate and butter in a microwave-safe bowl. Microwave for 1 minute; stir until well blended and smooth.
Place cereal in a large bowl. Pour chocolate mixture over top and toss to coat. You will have to stir quite a bit to make sure that all of the cereal squares are covered.
Once the cereal is coated, transfer the mixture to a large zip-top bag. Add dry cake mix, powdered sugar, and sprinkles to the bag; seal, and gently toss until all of the cereal is coated.
Stir in FLIPZ® Birthday Cake pretzels and marshmallows. Store in an airtight container until ready to serve.